The present invention relates to an image forming apparatus that forms an image on a sheet based on image data.
An image forming apparatus such as a copying machine and a printer is usually used ongoingly after installation, independently of a period of time after installation or after turning on electricity, or of the total hours of operation, unless it is disabled by troubles. However, from a viewpoint of a degree of safety, sufficient measures are not taken for troubles caused by deterioration of electric circuits mainly, especially of their constitutional parts, in the terminal stage of their lives, regarding safety measures in the case of occurrence of abnormal circumstances, although various protective circuits and safety devices are provided.
For this reason, when the apparatus is used, exceeding its mechanical life assumed at the time of design, there is a risk of occurrence of troubles caused by deteriorated parts for example, a decline of capacitance of a capacitor or removal of the soldered portion.
As an apparatus solving the aforesaid problems of mechanical life, there is given a power supply apparatus proposed in, for example, Unexamined Japanese Patent Application Publication No. 9-37461. In the power supply apparatus mentioned above, it is proposed to make it impossible to use the apparatus that has arrived at the end of its mechanical life, by providing an energization elapsed time measuring device that measures an energization period totally and a circuit operation stopping device that stops circuit operations through blowout of a fuse, on a power supply apparatus when the energization period exceeds a prescribed time.
Further, in Unexamined Japanese Patent Application Publication No. 54-153353, there is disclosed a proposed technology wherein the cooking time of a heating cooker, or the number of times of switching operations needed for cooking are totaled, and a power source is turned off when the cooking time or the number of switching operations arrives at a prescribed value.
In addition, Unexamined Japanese Patent Application Publication No. 4-80524, there is disclosed a proposed technology representing one described in Unexamined Japanese Patent Application Publication No. 54-153353 which has been improved not only to measure just only hours of use simply but also to correct the hours of use depending on levels of output in the course of operation.
However, each of all technologies shown in the aforesaid background art is one concerning measurement of life of such as a heating cooker, and a subject of measurement is substantially limited to the hours of operation of driving circuits for a heating device in the heating cooker. When operations of the aforesaid driving circuits are considered electrically, they represent mostly continuous working that is different from that of an image forming process in which various types of operations in an image forming apparatus are combined, thus, the aforesaid operations cannot be applied to the image forming apparatus.
In the case of an image forming apparatus, there are generated troubles caused not only by the hours of operation but also by temporal changes. When frequency in use for an image forming apparatus is low, many of parts constituting the apparatus preserve their sufficient capabilities even when the apparatus has been installed for considerable number of years, thus, a user judges that the apparatus has not arrived at the end of its life, and use of the apparatus is continued in many cases. Actually, however, in the case of an apparatus that has passed a prescribed period, the apparatus has some parts that have lost their safety as will be stated later. In this occasion, there are sometimes cases where the troubles are caused consequently.
A factor causing troubles in an image forming apparatus includes, for example, the followings. In a capacitor, a decline of capacitance proceeds by repetition of charge accumulation and charge emission. Though a semiconductor is housed usually in a resin package, it absorbs moisture with time, whereby, performance degradation is caused. In the soldered portion, cracks and removals are caused in addition to changes in resistance values caused by degeneration of the quality of the material for soldering. In the connector section, there is caused an increase of contact resistance resulted from oxidation on a surface. With respect to a motor, abrasion of a brush is caused when the motor is used, in the case of the so-called brush-type motor. In addition, in various portions of the circuit, declines of dielectric strength voltages on various insulated portions are caused by sticking and accumulation of dust.
In other words, in the image forming apparatus including electric circuits, there is a possibility of occurrence of troubles caused by temporal changes of circuits, independently of a energization period. For example, as stated above, resistance values are increased by degeneration of the quality of the material for soldering with the lapse of time in the soldered portion, and cracks and removals are caused on soldered joined portion by elastic forces of parts and of cables. Further, the so-called connectors are often used in these electric circuits, and their surfaces of contact portions are oxidized with the lapse of time, which sometimes causes generation of heat resulted from an increase of electrical resistance. In addition, sticking and accumulation of dust sometimes cause electric continuity between an electrically activated portion and a ground portion, depending on the state of installation.